Exemplary embodiments herein generally relate to a cooling structure for a front end of a vehicle. More particularly, the present disclosure is directed to a grille for a vehicle bumper configured to attenuate aerodynamically induced noises and sounds from the flow of air through the grille.
FIG. 1 is a perspective view of a vehicle 100 provided with a cooling structure 102. The vehicle 100 includes an engine compartment 110 provided at a front end of the body of the vehicle, a bumper 112 attached to a lower portion of the front end of the vehicle body and a grille 114 attached to an upper portion of the front end of the vehicle body. The bumper 112 has an elongated opening 116 formed in a central portion of a frontward protruding portion 118 of the front bumper 112, and the opening elongates in the transverse direction of the vehicle body. The opening 116 is defined by spaced transverse walls 120,120 and spaced apart side walls 122,122. A grille or mesh 128 is secured in the elongated opening 116. Left and right doors 130 are attached to the sides of the vehicle body. In the figure, reference numeral 132 denotes a bonnet, reference numeral 134 denotes a windshield, reference numerals 136,136 denote headlamps, and reference numerals 138,138 denote fog lights. As shown in FIG. 2, a radiator 150 is disposed rearward of the front bumper 112, i.e., below a front end portion of the bonnet 132 relative to the longitudinal direction of the vehicle body. This radiator 150 is cooled by cooling air introduced from the grille 114 and bumper grille 128. To secure the front bumper 112 to the vehicle body, a bumper beam 152 can be provided. Typically, the bumper beam 152 extends in the transverse direction of the vehicle body.
With particular reference to FIGS. 2-4, the bumper grille 128 includes an upper mesh part 160 and a lower mesh part 162, which is separated from the upper mesh part by a transverse member 164. The upper and lower mesh parts 160,162 direct cooling air toward a central portion of the radiator 150 and also shield the elongated opening 116 when viewed from the front of the vehicle body. The upper mesh part 160 includes a plurality of horizontal members 170 and a plurality of vertical members 172. As shown, the horizontal members 170 are in a stacked relationship to one another. The spaced apart vertical members 172 span between the upper transverse wall 120 and transverse member 164 and together with the horizontal members 170 define a plurality of stacked and transversely spaced rhombus shaped air passages 176. The lower mesh part 162 has a construction similar to the upper mesh part 160.
With this construction of the bumper grille 128, the upper and lower mesh parts 160,162 restrict the passage of particles to the vehicle radiator 150, thereby preventing large objects, such as rocks or road debris, from striking and damaging the vehicle radiator. However, as shown in FIG. 4, the flow of air through the upper mesh part 160 can create resonant vortices 180 downstream of the grille 128. These resonant vortices 180 can result in unwanted noises, such as a whistle sound, that is audible from the inside of the vehicle. Particularly, FIG. 5 graphically illustrates the whistle amplitude associated with the flow of air through the upper mesh part 160 of the grille 128. The solid line shows the sound amplitude of the air passing through the lower mesh part 162 of the bumper grille 128 with the upper mesh part 160 being masked. In the range of 2 kHz to 4 kHz, the sound or noise amplitude associated with the air flowing through the bumper grille 128 is about 55 dB, which is the sound amplitude of a normal conversation at 1 m. The dashed line shows the sound amplitude of the air passing through both the upper mesh part 160 and the lower mesh part 162 of the bumper grille 128. In the range of 2 kHz to 4 Khz, the sound or noise associated with the air flowing through the bumper grille 128 is about 79 dB, which is the sound amplitude of traffic on a busy roadway at 10 m. Because this whistle amplitude is audible within the vehicle cabin, it is desirable to mitigate or minimize the resonant vortices and the accompanying sounds associated with the cooling air passing through the bumper grille 128.